1. Field of the Invention
This invention relates generally to electric, liquid-filled tilt sensor devices, and more particularly to a rotation sensor which measures rotation about the axis normal to the circumferential plane of the sensor.
2. Brief Description of the Prior Art
Liquid filled tilt sensor and gravimeter devices are known in the art. There are several patents which various tilt sensor and gravimeter devices, none of which utilize electrical damping.
Cantarella et al, U.S. Pat. Nos. 4,167,818 and 4,244,117 discloses a gravity-sensing potentiometer mounted on a bar placed against a surface to be gauged to determine the degree to which the surface is inclined with respect to the horizontal and vertical axis to provide a digital or analog readout.
Thele, U.S. Pat. No. 4,121,347 discloses an apparatus for sensing and indicating the orientation of an object comprising two tilt sensing devices whose resistances vary responsive to the tilt of the devices, one of the sensing devices being mounted rotatably and connected by a bevel gear to the object being measured.
Shawhan, U.S. Pat. No. 3,906,471 discloses a capacitive type inclinometer which rotates with a portion of a drill pipe. A transmitter, located downhole near the inclinometer, converts the capacity changes of the inclinometer into a rectangular wave to be transmitted to the surface and read out as degrees.
Scopacasa, U.S. Pat. No. 3,786,472 discloses a toroid chamber half filled with mercury and having pairs of electrodes embedded in and spaced around the periphery of the chamber to correspond to the points of liquid contact when the chamber is inclined to predetermined angles.
Holderer, U.S. Pat. No. 3,164,023 discloses a motion sensing transducer comprising a toroid tubular member having a plurality of electrodes arranged to create an unbalanced condition in an electrical circuit repsonsive to deviation of position or movement of the device. The toroid tube is filled with a liquid and displaceable mass such as mercury which have different resistivity and are in contact with various electrodes in the normal position. Since the resistance of the liquid is greater than that of the mercury, the displacement of the mercury as the device is deviated from normal will increase or decrease the resistance between the electrodes.
Chaney, U.S. Pat. No. 3,984,918 discloses an inclinometer which employs a ferrofluid as a movable core of a differential transformer.
Lees, U.S. Pat. No. 2,983,149 discloses an angular accelerometer which is used to measure changes in angular velocity.
The present invention differs from the prior art in general and these patents in particular by providing a toroidal liquid filled sensor which measures rotation with respect to vertical in any plane normal to the earth's surface and comprises a sealed, non-conductive, hollow toroidal housing of square or rectangular cross section with an interior circular cavity or channel of like cross section. A discontinuous resistive strip circles the interior surface of the channel outer wall and a continuous conductive strip or collector circles the exterior surface of the channel inner wall. Electrical contacts are connected to each end of the resistive strip and a third contact is connected to the collector. The channel contains a quantity of dielectric fluid which has total volume less than a 30.degree. sector of the channel. Electrical damping (R-C time constant) is achieved by balancing the capacitance and resistance parameters. A single sensor has a linear range greater than 270.degree.. The combination of two sensors allows measurement of full 360.degree. of rotation and use of a sensor array allows measurement in 2 degrees of freedom for measuring pitch and roll.